The invention relates to a rack storage system with at least one storage and retrieval device, and to a method for controlling the movement path of a storage and retrieval device in a rack storage system.
Such a rack storage system accordingly comprises at least one storage and retrieval device with at least two movement axes which can be controlled independently of one another and are operated by means of electric motors, in order to carry out a movement from a starting point to a target point in order to transfer stored goods within the rack storage system and/or into or out of the rack storage system. Furthermore, an electric intermediate circuit for exchanging fed-back electrical energy is provided between the motors. By means of said intermediate circuit it is possible for the electrical energy which is fed back during braking of a movement axis by a generator-operating mode of the corresponding motor to be made available for consumption to the other motors. Finally, a control unit for controlling the motors of the movement axes of the storage and retrieval device is provided. This control unit pre-calculates the movement sequences, necessary for a movement from the starting point to the target point, of the individual movement axes, and coordinates them with one another. The motors of the movement axes are then actuated by the control unit in such a way that the storage and retrieval device carries out the movement on a pre-calculated movement path which is based on a set of movement sequences, coordinated with one another, of the individual movement axes.
The control unit just mentioned therefore implements a method of the type in question here. This is because in said method the movement sequences of the individual movement axes, which sequences are necessary for a movement of a storage and retrieval device with at least two movement axes which can be controlled independently of one another and are operated by means of electric motors, from a starting point to a target point, are pre-calculated and coordinated with one another. The motors of the movement axes are actuated in such a way that the storage and retrieval device carries out the movement on a pre-calculated movement path which is based on a set of movement sequences, coordinated with one another, of the individual movement axes.
Rack storage systems of the type in question here generally comprise a plurality of storage and retrieval devices which are each arranged so as to be movable in a rack aisle and can access each storage compartment of the rack aisle. As a result, automatic storage can be implemented in which, in particular, heavy stored goods, which cannot be moved manually, are stored. This rack storage system is particularly suitable for stored goods which must be accessed repeatedly, as is the case, for example, in the metal retail business. Stored metal rods, profiles and the like are kept available here in the rack storage system, in order to be removed, after the receipt of an order, from the rack storage system and fed, for example, to a sawing machine where the ordered quantity of the material is cut to length and put together with other ordered material. Residual pieces which remain after the cutting to length are then returned to storage in the rack storage system.
Such a rack storage system is operated with a central control system which actuates the individual storage and retrieval devices, with the result that existing orders are successively processed. For example, for one order it is necessary to extract a metal rod from a first storage compartment of a first rack aisle, to feed said metal rod to a sawing machine which is arranged in front of the rack aisle, to saw off a piece of the rod there and to return the rest of the rod back to storage, while a profile has to be extracted from a second storage compartment of another rack aisle and fed to the same sawing machine, in order also to saw off a piece from this profile and so on until the order is processed and the sawn-off pieces are put together in one order.
It is obvious that the rack storage system is more efficient the quicker the storage and retrieval device carries out the necessary movements from the starting point, for example the storage compartment, to the target point, for example a transfer point to the sawing machine. Therefore, in the prior art it has always been customary to actuate the motors of the individual movement axes of the storage and retrieval devices in each case at the maximum speed and with the maximum accelerations in order to carry out the movement as quickly as possible. However, this is not optimum under cost aspects, since the consumption of electrical energy with this procedure is also at a maximum. The simultaneous maximum acceleration of all the movement axes also causes disadvantageous peaks in the power consumption of the rack storage system.
WO-A-2008/025499 has therefore proposed that the control unit of a rack storage system of the type in question here be configured in such a way that for a movement of a storage and retrieval device from a starting point to a target point it firstly determines the time-critical movement axis, that is to say that movement axis, which, given a maximum speed of all the motors of the storage and retrieval device, requires the longest time for the necessary movement sequence. This would generally be that movement axis which has to travel the greatest distance; however, it can also be the slowest movement axis. This time-critical movement axis is actuated by the control unit with a maximum speed movement sequence, that is to say with a maximum speed of the associated motor and maximum accelerations. The remaining movement axes are controlled in a way which is optimized with respect to energy compared to the time-critical movement axis, with the result that the motors of the individual movement axes can mutually make available a maximum amount of braking energy. This means, in particular, that acceleration processes of the motors of the non-time-critical movement axes are preferably provided when electrical energy is fed back from the motor of the time-critical movement axis.
The prior art according to WO-A-2008/117248 therefore permits operation of a rack storage system whose requirement for electrical energy is advantageously reduced without adversely affecting the efficiency of the rack storage system, since the individual movements of the storage and retrieval devices are not slowed down overall compared to the practice hitherto.